52. Malignant Hyperthermia Flashcards
How does malignant hyperthermia present?
Rising end-tidal CO2 is one of the first signs
Tachycardia
Arrhythmias
Sweating
Muscle rigidity
Masseter spasm
Temperature rise
Not necessarily an early sign.
Rate of rise 2–5 ◦C/hour
You mentioned a raised ETCO2.
What are the causes of a raised ETCO2
A raised ETCO2 is not uncommon and may be due to:
Increased production
Hypermetabolic states, e.g. severe sepsis
Thyrotoxic crisis, MH
Reperfusion, e.g. cross-clamp release
Bicarbonate administration
Decreased excretion
Decreased minute volume
Exogenous administration
Laparoscopy, rebreathing
How would you differentiate MH from
other more common causes of a raised CO2?
What is the DDx
It is important to maintain a high index of suspicion of MH, being aware that
it has a high mortality if left untreated (70%) – and it is treatable.
Therefore, if the ETCO2 was high, one should exclude the more common causes of a raised ETCO2 such as rebreathing or a reduced minute volume.
The patient should be
observed for sweating, flushing and signs of cardiovascular instability.
Other differential diagnoses are:
Malignant neuroleptic syndrome
Ecstasy intoxication
Inadequate anaesthesia or analgesia.
How do you treat MH?
Stop administration of any likely causative agents (volatiles)
Change to a vapour-free machine and circuit. Use propofol/midazolam/
opioids to keep the patient asleep if needed.
Inform surgeons and abandon surgery if possible.
Summon help – both a senior and further skilled anaesthetic assistance.
Give 100% O2.
Hyperventilate – increase minute volume by 2–3 times.
Dantrolene give 2–3mg/kg i.v. initially and then 1mg/kg PRN.
Average dose needed to reverse MH crisis is 2.5 mg/kg.
Assistance will be needed to draw
this up, as it is slow to dissolve. Continue for 48 hours at a rate of 1–2 mg/kg
every 4–6 hours.
Measure core temperature
Cool the patient with ice/fan/tepid sponging/cold i.v. fluids and cold fluid
into the bladder if practical but avoid vasoconstriction. Cardiopulmonary
bypass has been used
Establish invasive monitoring: arterial line and CVP/PAFC
Check K+, CK and blood gases
Monitor coagulation profile for DIC
What is the molecular basis for the clinical picture?
(mainly autosomal dominant)
results in an error in skeletal muscle calcium control.
The inborn error leads to a loss of control of calcium
flux and an increase in the calcium concentration in the cytosol of skeletal
muscle.
The proposed site of action is the Ryanodine (a natural plant alkaloid)
receptor, which spans the calcium releasing channels on the sarcoplasmic
reticulum and T-tubule.
The increase in intracellular free calcium results in the clinical picture of:
Increased skeletal muscle contraction
Increased skeletal muscle metabolism
Glycolysis
Rhabdomyolysis
Uncoupling of oxidative phosphorylation
Dantrolene:
Vial containing orange powder
20mg per vial
3 g of mannitol (to improve solubility)
Sodium hydroxide (to give pH of 9.5)
Reconstitute with 60 ml of water
Protect from light
Testing for MH susceptibility:
Testing for MH susceptibility:
Halothane/caffeine/ryanodine
contracture testing – with a strain gauge
Muscle biopsy from vastus lateralis
Divides into:
MH susceptible – MHS
MH negative – MHN
MH equivocal – MHE
DNA testing is now available
